Ed,
I would expect condensation to form on these internal wall surfaces and
drain to the floor.If open meshed it will of course run through, if not its
useful to have a slight slope to the front so water cannot
accumulate.Condensation tends to happen whether painted internally or not. I
leave the two outer brood combs out ( Dadant 12-comb, single broodbox ) in
winter to help air circulation remove moisture.I have never painted hive
interiors, apart from floors.Some people here paint hive interiors with
alcoholic propolis solutions, after all, the bees coat  interior walls with
propolis anyhow which may well have bactericidal / fungicidal properties.I
am sure that open mesh floors help air circulation in winter.Whenever I give
the bees the choice of top ventilation in winter by placing wire mesh over
the feedhole ( my roofs have vents ) they always block it completely with
propolis so I gave up and don´t use top ventilation: I haven´t lost an
overwintering colony yet.I presume that condensation is also a function of
internal wall temp, the higher this is the more water the air can transport,
this infers that badly insulated walls will promote condensation in
winter.My walls are 22mm thick of a light firwood ( Weymuthkiefer ) with two
external coats of  Holzlasur ( this seems to be woodstain in the USA ). I
wonder if polystyrene hives with better insulation give similar problems.I
once measured winter air temps in Dadant wooden hives just over the cluster.
It was usually at least 6°C even when the outside temp was much lower.
Derek Steed

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